The present invention relates to a device for operating a swiveling or mobile body element intended for example to seal an access opening to a control or observation post. The device is constructed so that the mobile element can be moved angularly around a pivot pin extending into the body, by an operating handle operated from said post. The invention relates more particularly to the arrangement of the pivot pin and the operating handle which facilitates opening, closing and locking movements of the mobile element, and resists an accidental opening of the mobile element.